Browsing by Author "Bareither, Chris, committee member"

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Open Access
Environmental effects of the 1978 Sunnyside Mine flood
(Colorado State University. Libraries, 2024) Arnold, Victoria S., author; Ridley, John, advisor; Wohl, Ellen, committee member; Bareither, Chris, committee member
In 1978, the pillar of rock and sediment between Lake Emma and the Sunnyside Mine collapsed, draining 5-25 M gallons (19-95 ML) of water and sediment through the mine and the American Tunnel within a few hours (Thompson, 2018). This caused a major flood in Cement Creek, a tributary of the Animas River north of Silverton, Colorado. Although work has been done on the geochemistry of mine outwash in the same drainage from the 2015 Gold King Mine spill, the material from the Sunnyside Mine flood has not been extensively studied previously. This study aims to determine whether the 1978 Sunnyside Mine flood had significant geochemical and geomorphic effects and continues to affect the environment today. Likely flood deposits were identified approximately fifteen centimeters above the typical spring flood level based on sediment characteristics, interviews with witnesses to the flood and community stakeholders, as well as newspaper articles and photographs from shortly after the flood. Cement Creek sediment samples from flood and non-flood deposits were analyzed with VNIR spectroscopy for mineralogy. Sediment samples from the Sunnyside flood contained vermiculite, iron smectite, zeolites, gypsum, and secondary copper minerals, while most stream sediment included ferrihydrite, K-illite, and vermiculite. Sediment samples were also analyzed for their bulk elemental geochemistry, which revealed that the Sunnyside flood sediments had lower concentrations of heavy metals than the other sediments in Cement Creek, but had 59% more iron and 518% more sulfur. It is not clear whether the increased iron and sulfur exist as unweathered sulfides or as sulfates, but if there are sulfides or secondary sulfate minerals present in the flood sediment, then the flood sediment has significantly more acid generation potential than the other sediment in Cement Creek. Additionally, the average Fe/Cu ratios of the flood sediment is higher than the non-flood sediment, which indicates that the material is either from a different source, or that the flood water had lower pH than the water in Cement Creek when the other sediments were deposited. The significant difference in the minerals present and the elemental geochemistry, as well the continued preservation of flood horizon sediments, indicate that the Sunnyside Mine flood impacted the Cement Creek watershed. Understanding the impact that a major disaster like the Sunnyside Mine flood had on the area is important to have a better picture of a region that continues to face environmental impacts from mining activities.
Open Access
Failure mode analysis of a post-tension anchored dam using linear finite element analysis
(Colorado State University. Libraries, 2014) Corn, Aimee, author; Heyliger, Paul, advisor; Bareither, Chris, committee member; Glick, Scott, committee member; Lund, Guy, committee member
There are currently over 84,000 dams in the United States, and the average age of those dams is 52 years. Concrete gravity dams are the second most common dam type, with more than 3,000 in the United States. Current engineering technology and technical understanding of hydrologic and seismic events has resulted in significant increases to the required design loads for most dams; therefore, many older dams do not have adequate safety for extreme loading events. Concrete gravity dams designed and constructed in the early 20th century did not consider uplift pressures beneath the dam, which reduces the effective weight of the structure. One method that has been used to enhance the stability of older concrete gravity dams includes the post-tension anchor (PTA) system. Post-tensioning infers modifying cured concrete and using self-equilibrating elements to increase the weight of the section, which provides added stability. There is a lack of historical evidence regarding the potential failure mechanisms for PTA concrete gravity dams. Of particular interest, is how these systems behave during large seismic events. The objective of this thesis is to develop a method by which the potential failure modes during a seismic event for a PTA dam can be evaluated using the linear elastic finite element method of analysis. The most likely potential failure modes (PFM) for PTA designs are due to tensile failure and shear failure. A numerical model of a hypothetical project was developed to simulate PTAs in the dam. The model was subjected to acceleration time-history motions that simulated the seismic loads. The results were used to evaluate the likelihood of tendon failure due to both tension and shear. The results from the analysis indicated that the PTA load increased during the seismic event; however, the peak load in the tendons was less than the gross ultimate tensile strength (GUTS) and would not be expected to result in tensile failure at the assumed project. The analysis also indicated there was a potential for permanent horizontal displacement along the dam/foundation interface. The horizontal movement was not considered large enough to develop a shear failure of the tendons at the project. The results from this study indicate demand to capacity ratios (DCR) of 0.79 for the anchor head, 0.75 for the tendon, and 0.63 for the foundation cone failure, and a potential displacement of 0.33 inches, which is not large enough to shear the tendon. The methods developed are appropriate for the evaluation of the tensile and shear failure modes for the PTA tendons. Based on the results, it would appear that shear failure of the tendon is a more likely failure mechanism. Thus, shear failure of the tendon should be a focus of seismic evaluations.